import * as Cesium from '@cesiumjs';

const $defaultOpts = {
  size: 0.02, //最好小于0.02
  speed: 60.0,
}

class SnowEffect {

  constructor(viewer, options) {
    if (!viewer) {
      console.error('no viewer object!')
      throw new Error('no viewer object!')
    };
    this._viewer = viewer;
    this.stage = undefined;
    this.options = { ...$defaultOpts, ...options}

    this.defineProperties();
    this.init();
  }

  defineProperties() {
    const _this = this;
    const {options:opt} = this;
    Object.defineProperty(this, "size", {
      get(){return opt.size;},
      set(val){ opt.size = val }
    })
    Object.defineProperty(this, "speed", {
      get(){return opt.speed;},
      set(val){ opt.speed = val }
    })
    Object.defineProperty(this, "show", {
      get(){return _this.stage&&_this.stage.enabled;},
      set(val){ _this.stage&&(_this.stage.enabled = val) }
    })
    Object.defineProperty(this, "viewer", {
      get(){return _this._viewer;}
    })
  }

  init() {
    this.destroy();

    this.stage = new Cesium.PostProcessStage({
      name: 'czm_snow',
      fragmentShader: this.snow(),
      uniforms: {
        size: () => {
          return this.size;
        },
        speed: () => {
          return this.speed;
        }
      }
    });

    this.viewer.scene.postProcessStages.add(this.stage);
  }

  destroy() {
    const {viewer,stage} = this;
    stage && viewer.scene.postProcessStages.remove(stage);
    // stage && stage.destroy();
    this.stage = null;
  }

  // show(visible) {
  //   this.snowStage.enabled = visible;
  // }

  snow() {
    return "uniform sampler2D colorTexture;\n\
      varying vec2 v_textureCoordinates;\n\
      uniform float speed;\n\
      uniform float size;\n\
      float snow(vec2 uv,float scale)\n\
      {\n\
          float time=czm_frameNumber/speed;\n\
          float w=smoothstep(1.,0.,-uv.y*(scale/10.));if(w<.1)return 0.;\n\
          uv+=time/scale;uv.y+=time*2./scale;uv.x+=sin(uv.y+time*.5)/scale;\n\
          uv*=scale;vec2 s=floor(uv),f=fract(uv),p;float k=3.,d;\n\
          p=.5+.35*sin(11.*fract(sin((s+p+scale)*mat2(7,3,6,5))*5.))-f;d=length(p);k=min(d,k);\n\
          k=smoothstep(0.,k,sin(f.x+f.y)*size);\n\
          return k*w;\n\
      }\n\
      void main(void){\n\
          vec2 resolution=czm_viewport.zw;\n\
          vec2 uv=(gl_FragCoord.xy*2.-resolution.xy)/min(resolution.x,resolution.y);\n\
          vec3 finalColor=vec3(0);\n\
          //float c=smoothstep(1.,0.3,clamp(uv.y*.3+.8,0.,.75));\n\
          float c=0.;\n\
          c+=snow(uv,30.)*.0;\n\
          c+=snow(uv,20.)*.0;\n\
          c+=snow(uv,15.)*.0;\n\
          c+=snow(uv,10.);\n\
          c+=snow(uv,8.);\n\
          c+=snow(uv,6.);\n\
          c+=snow(uv,5.);\n\
          finalColor=(vec3(c));\n\
          gl_FragColor=mix(texture2D(colorTexture,v_textureCoordinates),vec4(finalColor,1),.5);\n\
      }";
  }
}

export default SnowEffect;
